Water-Related Ecosystem Services of Forests: Learning from Regional Cases
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PART II – Chapter 27 Water-related ecosystem services of forests: Learning from regional cases Convening lead author: Bart Muys Lead authors: Jan Nyssen, Ben du Toit, and Enrico Vidale Contributing authors: Irina Prokofieva, Robert Mavsar, and Marc Palahi Abstract: Forests are widely recognised as recommended land cover for protection of water resources. It is commonly understood that forests control erosion, improve water quality and regulate water flows in catchments to some extent. Less-well understood are aspects of the so-called green water flow: biomass production in forests has a price locally in terms of evaporative water losses though it can provide rainfall elsewhere. In this chapter, we discuss the complex and sometimes contra-intuitive issues that emerge when trying to optimise forest management for water-related ecosystem services. We analyse three cases in very different geographical and socio-economic settings where the water-related ecosystem services of the forest have been a driver for forest man- agement transition. In the first example from Ethiopia, forests are restored for soil and water conservation purposes related to green water, while in the second case in South Africa, plantation forests are removed with the intention of ecological restoration and increase in blue water availability. In the last case from Italy, we discover that schemes for payment for ecosystem services (PES) make a change with respect to water-related ecosystem services. The case studies show that such transitions can follow very different pathways, determined by the biophysical, socio-economic, and institutional contexts. But despite these differences, the case studies show patterns in common. The success or failure of management policies is highly scale-dependent (extension and intensity of the intervention). Changes aimed at improving an ecosystem service always show trade-offs with other ecosystem services. Often, measures in catchments are based on a correct interpretation of hydrological knowledge but fail to optimise for the range of upstream and downstream ecosystem services at stake. The main challenge for the future is to further foster the ongoing paradigm shift in the way water-related forest ecosystems services are considered, with a change from supply-side policies to demand-side policies and supply-demand linkages and from purely technical solutions to green infrastructure solutions. Keywords: Blue water, green water, South Africa, Ethiopia, Italy, water tax, exclosure, payment for ecosystem services 27.1 Introduction to water- supported by available data. Forests may increase low flows but in most cases they decrease them related ecosystem services (Jackson et al. 2005, Birot et al. 2011). For a better understanding of the hydrological cycle, distinguish- resh water is becoming a scarce global resource ing between blue and green water (Falkenmark and Fof strategic importance (Duda and El-Ashry Rockstrøm 2005, Birot et al. 2011) is very useful. 2000). In this context, the regulating role of forests Blue water resources are formed by the rainfall frac- has been recognised (de Groot et al. 2010), although tion that reaches rivers and lakes after percolation 423 the sponge model – the general belief that forests into the aquifers or directly as surface run-off. Hu- store water in the rainy season to slowly release it mans strongly value the quantity and quality of blue in the dry season (e.g. Hamilton 1985) – is not much water, as it forms the main source for drinking water, PART II: CASE STUDIES 27 WATER-related ECOSYSTEM SERVICES OF FORESTS: LEARNING froM REGIONAL cases Table II 27.1 Overview of the main water-related ecosystem services of a forest. ECOSYSTEM SERVICES (ES) MAIN WATER-RELATED ES OF A FOREST (Green water services in bold, blue water services in italic, green/blue water services underlined) Supporting services (S) Canopy interception, Evapotranspiration Provisioning services (P) Irrigation water provision, drinking water provision, fish production, wood production Regulating services (R) Flood regulation, climate regulation, erosion control, water purification Cultural services (C) Recreation, ecotourism irrigation water, hydropower, and recreational activi- To consider trade-offs between green and blue ties. Green water resources are formed by the fraction water use, the ecosystem services framework pro- of rainfall that does not leave the ecosystem through posed by the Millennium Ecosystem Assessment percolation or surface run-off. It may infiltrate into (MEA 2005) can serve as an excellent basis. MEA the soil and become available for uptake by plants. (2005) considers supporting, provisioning, regulat- The green water flow is the evapotranspiration of this ing, and socio-cultural services. Table II 27.1 shows green water resource into the atmosphere. Precipita- the water-related ecosystem services in each of these tion water intercepted by vegetation canopies forms categories. Based on the aforementioned blue and part of green water resources, and its evaporation is green water definitions, we can now distinguish a green water flow. The green water flow includes between blue water services of the forest (here de- the evapotranspiration from blue water resources as fined as ecosystem services provided by the forest, well, such as irrigation water used by crops and the related to the availability and quality of blue water so-called virtual water incorporated in imported and resources), green water services (here defined as exported products like wood, food, and feed (Allan ecosystem services provided by the forest, related 1998). to the availability of green water resources or the Compared with other land uses, forests typical- existence of green water flows), and green/blue ly have larger green water and smaller blue water water services providing both (Table II 27.1). As fractions, which means that afforestation generally a supporting ecosystem service, evapotranspiration decreases blue water quantities and deforestation in- is the driving process behind green water flows, but creases them. Today there is a dominant blue water water interception by vegetation canopies is also an paradigm that considers green water flows and thus important process that will, for example, diminish the very existence of forests as a water loss. But the erosive power and influence the quality of pre- this paradigm largely ignores the important ecosys- cipitation water. Wood production is a provisioning tem services related to green water flows, including service of the forest typically linked to green water biomass production, erosion control, and nutrient flows, except when the water transpiration by the retention (Birot and Vallejo 2011). Recent research plant originates from irrigation water. Water puri- has quantified the essential function of green water fication is both a green- and blue-water regulating flows for precipitation recycling and relocation over service, as both vegetative processes by canopies and continents (Keys et al. 2012). roots and filtering processes in the lithosphere and Both blue and green water flows are essential for surface waters can have a purifying effect. sustainable catchment management. There is a direct In this chapter we discuss the complex and some- trade-off between green and blue water use, and de- times contra-intuitive issues that emerge when trying velopment in either direction (blue water maximisa- to optimise forest and land management for water- tion by, for example, impeding forest restoration, or related ecosystem services. To do this, we analyse green water maximisation by establishment of fast- three cases in very different geographical and socio- growing exotic tree plantations) has tangible effects economic settings where the water-related ecosys- on the other. For this reason sustainable management tem services of the forest have been the driver for a 424 of river catchments must take an integrated approach transition in forest management or conservation. In in which the ecosystem services of upstream (terres- the first example from Ethiopia, forests are restored trial) and downstream (aquatic) ecosystem services for soil and water conservation purposes related to are considered together (Maes et al. 2009). green water, while in the second case in South Af- FORESTS UNDER PRESSURE – LOCAL RESPONSES TO GLOBAL ISSUES 27 Water-RELated ECOSYSTEM SERVICES OF FORESTS: LEARNING FROM REGIONAL cases 27 WATER-RELated ECOSYSTEM SERVICES OF FORESTS: LEARNING FROM REGIONAL cases Figure II 27.1 Map of the study area in Tigray, Ethiopia showing the six major land-use and cov- er-change trajectories for 1972–2000, indicated by different colours (after de Mûelenaere et al. 2014. ©Reprinted with permission from John Wiley & Sons, Inc. rica, plantation forests are removed with the intention temperate climate than would normally be associ- of ecological restoration and increase of blue water ated with the latitude. Average yearly rainfall ranges availability. In the last case from Italy, payment for between 500 and 900 mm/year, with a uni-modal ecosystem services (PES) schemes make a change pattern. Time series analysis of annual precipitation with respect to water-related ecosystem services. shows that although the succession of dry years in the Ethiopian highlands between the late 1970s and late 1980s produced the driest decade in the previous 27.2 Soil and water century, there is no evidence for a long-term trend or change in the region’s annual rain regime (Nyssen conservation: